This crystal skull was anonymously mailed to the Smithsonian Institution in 1992. A letter included with the artifact said it was from the Aztec empire.
Jim DiLoreto/Smithsonian Institution
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Jim DiLoreto/Smithsonian Institution

This crystal skull was anonymously mailed to the Smithsonian Institution in 1992. A letter included with the artifact said it was from the Aztec empire.

Anthropologist Jane MacLaren Walsh and Scott Whittaker from the Smithsonian Institution examine a smaller crystal skull under the microscope.

Jim DiLoreto/Smithsonian Institution

A swashbuckling archaeologist returns to the big screen next week, in Indiana Jones and the Kingdom of the Crystal Skull. As the title suggests, the precious artifact this time around is a crystal skull. In reality, crystal skulls are immersed in intrigue — and not just the kind Hollywood would have you believe.

Some of the skulls are in museums; others are held by private collectors. The largest known specimen can be found at the Smithsonian Institution's National Museum of Natural History in Washington, D.C. But you won't see it on display. You have to wend your way down a long hallway lined with ceiling-high cabinets filled with human bones. In a back office, inside a locked filing cabinet, the skull is in the care of anthropologist Jane Walsh.

"This is actually called milky quartz," Walsh explains as she gingerly lifts the carved quartz skull out of a drawer. It's the size of a bowling ball, smooth as ice, with hollow eye sockets. "It weighs 31 pounds," she says. "I know because I carried it to London."

This skull was mailed to the Smithsonian in 1992. The anonymous donor said it was a genuine artifact of the Aztec empire, which collapsed in the 1500s.

Walsh wondered if her skull was the real McCoy.

She did some reading and discovered that there are dozens of crystal skulls around the world. Most are quite small, the size of golf balls. They started to appear in the antiquities trade in the 1860s. Several were sold from Mexico by a French collector named Eugene Boban.

Revealing Origins

But Walsh's studies didn't shed light on the big question: Could the Aztecs have carved these pieces? Walsh studied the kinds of tools the Aztecs used to carve stone, such as the pump drill, a wood-and-rope contraption that spins a wooden rod with a stone tip. Such tools left distinctive marks, different from those left by modern tools such as fast-spinning rotary wheels.

Walsh needed someone to help analyze the skull, so she took it to Margaret Sax at the British Museum in London. Sax is an expert on markings from carving and polishing. She examined the tool marks under a powerful scanning electron microscope, just as she had done with another big crystal skull her museum had owned for over a century. It, too, was supposed to be ancient Mexican.

But just like the British specimen, Walsh's artifact wasn't authentic.

"The tool marks on both the Smithsonian skull and the British Museum skull were clearly produced by wheel cutting," she says, "and so we are able to say they are of post-Columbian date." The marks' shape, depth and surface texture indicated the skulls had been made by rotary tools, and no one in Central or South America was known to have those until Europeans arrived.

Now Walsh and Sax are looking at the type of quartz from which the skulls are made. Small imperfections could help identify where it came from. They say neither of the two skulls is likely from Mexico, home of the Aztecs.

An Invented Artifact

One thing the scientists have figured out is that the British Museum's skull came from Boban, that mysterious French collector. In the late 1800s, he first described it as a piece of artwork. Then he began calling it an Aztec artifact, in an attempt, Sax says, to make it "more appealing in order to sell it."

So, what are these things? Walsh says they're not exactly "fakes" because they aren't copies of anything.

"I don't think there are any real ones," she explains. "They're really a kind of invented artifact. ... Some person or some workshop was cranking them out and selling them to a European or North American audience, which is where they all wind up."

Eventually, they wind up locked away in the bowels of a museum.

Walsh returns the skull to its place in the drawer. "We should have him face out," she says, and then laughs. "People keep telling me not to look it in the eye."